Portable information appliances, including personal digital assistants (PDA's), portable PCs, cell phones, digital watches, laptops, etc. are valued because they are small and portable. All else being equal, the smaller these devices are the more valuable they are except for the human interface such as the display. Generally, consumers want bigger displays with more pixels so that more information can be displayed on a single screen. Depending on the function of the portable information appliance, there is often a balance that must be struck between portability and viewing area.
A PDA (e.g., Palm®) is an example of a portable information appliance that may strike such a balance. The PDA often fits into a shirt pocket and has a screen of about 3″×3″ and 160×160 pixels. While highly functional for many applications, including listing contact information, tasks and notes, it has proven difficult to use for a wide range of other applications. Full web pages, images like photos or maps, or large forms or schematic diagrams cannot readily be viewed on such small screens. Scroll functions are often available, but rarely used because the user tends to easily get lost while pushing the document up and down across the display surface. In short, it is often difficult to envision the document without a point of reference or some mnemonic.
For those applications where it is desirable to view larger documents or objects, handheld computers and laptops, which have bigger screens, have been the traditional solution. Between these two extremes, however, there are a vast number of applications that cannot readily be accommodated.